Process for improving water-whitening resistance of pressure sensitive adhesives

ABSTRACT

Pressure sensitive adhesive compositions having enhanced resistance to water-whitening comprising an aqueous emulsion polymer are disclosed. The polymer comprises the polymerization reaction product of a polymerizable aqueous emulsion comprising: (i) at least one hydrophobic alkyl acrylate or alkyl methacrylate ester of an alcohol, (ii) at least about 1 wt. % of at least one hydrophilic monomer, (iii) at least about 5 wt. % of at least one partially hydrophilic alkyl acrylate or alkyl methacrylate ester of an alcohol, and (iv) a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, substituted phenyl compounds having at least one alkenyl substituent, polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixtures thereof, and the average particle size of the polymer is less than or equal to 200 nm. Also disclosed are processes for preparing same.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of nonprovisionalapplication Ser. No. 10/142,455, filed May 10, 2002, which claims thepriority of prior provisional applications Ser. No. 60/305,174, filedJul. 13, 2001 and Ser. No. 60/323,984, filed Sep. 21, 2001, thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to pressure sensitive adhesives based on aqueousemulsions and processes for preparation of the adhesives. The pressuresensitive adhesives of the invention have enhanced resistance towater-whitening.

These pressure sensitive adhesives are particularly suitable forapplications that require that the pressure sensitive adhesive maintainadhesion between the substrate and facestock when subjected to hot waterspraying or immersion. Hot water adhesion is required in applicationssuch as bottle labels where the bottles are subjected to hot waterspraying in washing operations. In general, resistance towater-whitening is desirable anywhere a pressure sensitive adhesive withtransparent facestock or substrate is subjected to water or highhumidity. Examples include labels on the sides of trucks, signs andbottles.

Methods of providing water-whitening resistant latex emulsions for usein pressure sensitive adhesives are disclosed in the art. U.S. Pat. No.5,286,843 discloses a process for improving the water-whiteningresistance of pressure sensitive adhesives containing an aqueous latexemulsion and water soluble ions by removing the water soluble ions andadjusting the pH to at least about 6. The patent discloses that watersoluble ions may be removed by a number of techniques includingcentrifugation, dialysis, precipitation and deionization with ionexchange resins. The preferred method of removing the water soluble ionsis to contact the aqueous latex emulsion, the formulated pressuresensitive adhesive containing the aqueous emulsion or both with an ionexchange resin. International Publication No. WO 97/11996 discloses aprocess for preparing hot water-whitening resistant latex emulsionsuseful in pressure sensitive adhesive compositions. The process involvescopolymerizing a monomer mixture containing at least one alkyl acrylateester of an alcohol containing at least 4 carbon atoms, at least onepolar co-monomer, and at least one partially water-soluble co-monomerpresent in an amount of at least about 7 wt. %. Polymerization iscarried out in the presence of at least one nonionic surfactantcontaining at least 8 moles of ethylene oxide and at least one anionicsurfactant containing up to about 10 moles of ethylene oxide. Thepolymerization product is neutralized to produce an emulsion having a pHgreater than 7 and containing particles having a volume average particlesize diameter up to about 165 nm. An electrolyte may be added subsequentto polymerization to stabilize opacity of a film cast from the emulsion.International Publication No. WO 00/61670 discloses a process forpreparing an aqueous latex emulsion for use in pressure sensitiveadhesives that maintain adhesion in hot water environments in additionto exhibiting enhanced resistance to water-whitening. The processinvolves preparing an aqueous latex emulsion from a monomer mixtureconsisting essentially of at least one alkyl acrylate having at least 4carbon atoms in the alkyl chain, at least one ethylenically unsaturatedcarboxylic acid, and at least one styrenic monomer, the polymerizationbeing carried out in the presence of at least one anionic surfactant anda redox type free radical initiator system. The aqueous latex emulsionprepared according to the process of WO 00/61670 is disclosed to havepolymer particles with a mean particle size diameter of less than orequal to about 100 nm. None of the above patents/publications disclosepreparing pressure sensitive adhesives wherein a polymerizablesurfactant is used.

U.S. Pat. Nos. 5,928,783 and 6,239,240 disclose processes for preparingaqueous emulsion polymers that have application as pressure sensitiveadhesives. The polymers are prepared by reacting at least oneethylenically unsaturated monomer and a polymerizable surfactant havinga terminal allyl amine moiety. Neither patent discloses preparation ofpressure sensitive adhesives having enhanced resistance towater-whitening.

SUMMARY OF THE INVENTION

It is an object of this invention to provide pressure sensitive adhesive(“PSA”) compositions having enhanced resistance to water-whitening. Itis another object of this invention to provide a process(es) forpreparing pressure sensitive adhesives having enhanced resistance towater-whitening.

These and other objects are achieved in the invention which is describedin more nonlimiting detail hereinafter.

According to the invention, a process for preparing a pressure sensitiveadhesive having enhanced resistance to water-whitening is providedcomprising: (a) forming a polymerizable aqueous pre-emulsion comprising:(i) at least one hydrophobic alkyl acrylate or alkyl methacrylate esterof an alcohol, (ii) at least about 1 wt. % of at least one hydrophilicmonomer, (iii) at least about 5 wt. % of at least one partiallyhydrophilic alkyl acrylate or alkyl methacrylate ester of an alcohol,and (iv) a water-soluble or water-dispersible polymerizable surfactantselected from compounds having a terminal allyl amine moiety,substituted phenyl compounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, wherein the wt. % of monomers (i), (ii) and (iii) are based onthe total weight of monomers (i), (ii) and (iii) in the pre-emulsion;(b) contacting water, an effective amount of a water-soluble orwater-dispersible polymerizable surfactant selected from compoundshaving a terminal allyl amine moiety, substituted phenyl compoundshaving at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, and an initial amount of polymerization initiator to form amixture; (c) continuously adding the pre-emulsion to the mixture of (b)to polymerize the pre-emulsion to form a latex emulsion, whereinadditional polymerization initiator is added during the polymerizationof the pre-emulsion; and (d) adjusting the pH of the latex emulsion witha suitable base to a pH of about 6.5 to about 9; wherein the effectiveamount of water-soluble or water-dispersible polymerizable surfactant inthe mixture of (b) is that amount necessary to produce pressuresensitive adhesive having an average particle size of less than or equalto 200 nm.

Further according to the invention, a process for preparing a pressuresensitive adhesive having enhanced resistance to water-whitening isprovided comprising: (a) contacting water, an effective amount of awater-soluble or water-dispersible polymerizable surfactant selectedfrom compounds having a terminal allyl amine moiety, substituted phenylcompounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, and an initial amount of polymerization initiator to form amixture; (b) continuously adding monomers and, optionally, additionalwater to the mixture and polymerizing the resultant emulsion to form alatex emulsion, wherein additional polymerization initiator is addedduring the polymerization of the emulsion, and wherein the monomerscomprise: (i) at least one hydrophobic alkyl acrylate or alkylmethacrylate ester of an alcohol, (ii) at least about 1 wt. % of atleast one hydrophilic monomer, (iii) at least about 5 wt. % of at leastone partially hydrophilic alkyl acrylate or alkyl methacrylate ester ofan alcohol, and (iv) a water-soluble or water-dispersible polymerizablesurfactant selected from compounds having a terminal allyl amine moiety,substituted phenyl compounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, wherein the wt. % of monomers (i), (ii) and (iii) are based onthe total weight of monomers (i), (ii) and (iii); and (c) adjusting thepH of the latex emulsion with a suitable base to a pH of about 6.5 toabout 9; wherein the effective amount of water-soluble orwater-dispersible polymerizable surfactant in the mixture is that amountnecessary to produce the pressure sensitive adhesive having an averageparticle size of less than or equal to 200 nm.

Further according to the invention, pressure sensitive adhesivecompositions having enhanced resistance to water-whitening comprising anaqueous emulsion polymer are provided, the polymer comprising thepolymerization reaction product of a polymerizable aqueous emulsioncomprising: (i) at least one hydrophobic alkyl acrylate or alkylmethacrylate ester of an alcohol, (ii) at least about 1 wt. % of atleast one hydrophilic monomer, (iii) at least about 5 wt. % of at leastone partially hydrophilic alkyl acrylate or alkyl methacrylate ester ofan alcohol, and (iv) a water-soluble or water-dispersible polymerizablesurfactant selected from compounds having a terminal allyl amine moiety,substituted phenyl compounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, wherein the wt. % of monomers (i), (ii) and (iii) are based onthe total weight of monomers (i), (ii) and (iii); wherein after thepolymerization the pH of the polymer is adjusted to a pH of about 6.5 toabout 9, and the average particle size of the polymer is less than orequal to 200 nm.

Still further according to the invention, pressure sensitive adhesiveshaving enhanced resistance to water-whitening produced by theprocess(es) described above are provided.

Optionally included in the process of the invention is the addition of avinyl ester of a C₂ to C₁₀ carboxylic acid to the latex emulsion afterthe conversion of monomers (i), (ii) and (iii) is greater than 90%. Theinvention also optionally provides pressure sensitive adhesives whereinthe polymerization reaction product further comprises a vinyl ester of aC₂ to C₁₂ carboxylic acid that is added to the polymerization reactionproduct after the conversion of monomers (i), (ii) and (iii) is greaterthan 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

In describing the invention, reference will be made to FIG. 1 which is agraph showing the change in absorbance over a 24 hour period of direct-and transfer-coated pressure sensitive adhesives of the invention(curves 1 and 2) versus a control pressure sensitive adhesive preparedusing conventional surfactants (curve 3).

DETAILED DESCRIPTION OF THE INVENTION

This invention provides aqueous emulsion pressure sensitive adhesivesuseful in the production of products such as labels, decals and thelike, particularly label and decal facestock that are at least partiallytransparent, and are subject to water or high humidity during use. Thepressure sensitive adhesives of the invention are particularly useful inbottle label applications where the labeled bottles are subject to hotwater environments.

The pressure sensitive adhesives of the invention exhibit enhancedresistance to water-whitening. The extent of water-whitening can bedetermined visually or by using UV/Visible spectroscopy measuringabsorbance as a function of time. As used herein, the PSA's of theinvention were determined to have an acceptable level of water whiteningof the PSA film when (a) the increase of absorbance was less than 0.2,preferably less than 0.05, after 24 hour room temperature waterimmersion (as determined by UV/Visible spectroscopy), and/or (b) therewas no visible change after 30 min. immersion in 190° F. (87.8° C.)water.

A first embodiment of the invention relates to a process for preparing apressure sensitive adhesive having enhanced resistance towater-whitening comprising: (a) forming a polymerizable aqueouspre-emulsion comprising: (i) at least one hydrophobic alkyl acrylate oralkyl methacrylate ester of an alcohol, (ii) at least about 1 wt. % ofat least one hydrophilic monomer, (iii) at least about 5 wt. % of atleast one partially hydrophilic alkyl acrylate or alkyl methacrylateester of an alcohol, and (iv) a water-soluble or water-dispersiblepolymerizable surfactant selected from compounds having a terminal allylamine moiety, substituted phenyl compounds having at least one alkenylsubstituent, polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfatesalts, or mixtures thereof, wherein the wt. % of monomers (i), (ii) and(iii) are based on the total weight of monomers (i), (ii) and (iii) inthe pre-emulsion; (b) contacting water, an effective amount of awater-soluble or water-dispersible polymerizable surfactant selectedfrom compounds having a terminal allyl amine moiety, substituted phenylcompounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, and an initial amount of polymerization initiator to form amixture; (c) continuously adding the pre-emulsion to the mixture of (b)to polymerize the pre-emulsion to form a latex emulsion, whereinadditional polymerization initiator is added during the polymerizationof the pre-emulsion; and (d) adjusting the pH of the latex emulsion witha suitable base to a pH of about 6.5 to about 9; wherein the effectiveamount of water-soluble or water-dispersible polymerizable surfactant inthe mixture of (b) is that amount necessary to produce pressuresensitive adhesive having an average particle size of less than or equalto 200 nm, preferably less than or equal to 100 nm.

A second embodiment of the invention relates to a process for preparinga pressure sensitive adhesive having enhanced resistance towater-whitening comprising: (a) contacting water, an effective amount ofa water-soluble or water-dispersible polymerizable surfactant selectedfrom compounds having a terminal allyl amine moiety, substituted phenylcompounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, and an initial amount of polymerization initiator to form amixture; (b) continuously adding monomers and, optionally, additionalwater to the mixture and polymerizing the resultant emulsion to form alatex emulsion, wherein additional polymerization initiator is addedduring the polymerization of the emulsion, and wherein said monomerscomprise: (i) at least one hydrophobic alkyl acrylate or alkylmethacrylate ester of an alcohol, (ii) at least about 1 wt. % of atleast one hydrophilic monomer, (iii) at least about 5 wt. % of at leastone partially hydrophilic alkyl acrylate or alkyl methacrylate ester ofan alcohol, and (iv) a water-soluble or water-dispersible polymerizablesurfactant selected from compounds having a terminal allyl amine moiety,substituted phenyl compounds having at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, wherein the wt. % of monomers (i), (ii) and (iii) are based onthe total weight of monomers (i), (ii) and (iii) added to the mixture;and (c) adjusting the pH of the latex emulsion with a suitable base to apH of about 6.5 to about 9; wherein the effective amount ofwater-soluble or water-dispersible polymerizable surfactant in themixture is that amount necessary to produce the pressure sensitiveadhesive having an average particle size of less than or equal to 200nm, preferably less than or equal to 100 nm.

Hydrophobic alkyl acrylate or alkyl methacrylate ester monomers that canbe employed according to the invention include alkyl acrylate or alkylmethacrylate esters of an alcohol wherein the alkyl portion of thealcohol is linear or branched and contains at least 4 carbon atoms. Thealkyl groups of the alkyl acrylate or alkyl methacrylate monomers arepreferably linear or branched alkyl radicals having from 4 to about 14carbon atoms, more preferably from 4 to about 10 carbon atoms, and mostpreferably from 4 to about 8 carbon atoms. Examples of this class ofmonomers include, but are not limited to, isooctyl acrylate,4-methyl-2-pentyl acrylate, 2-methyl-butyl acrylate, isoamyl acrylate,sec-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isodecylmethacrylate, isononyl acrylate, isodecyl acrylate, and the like, singlyor in mixtures of two or more.

The currently preferred hydrophobic monomers are 2-ethylhexyl acrylate,n-butyl acrylate, and mixtures thereof.

The amount of hydrophobic alkyl acrylate or alkyl methacrylate estermonomers based on the total weight of monomers (i), (ii) and (iii) ispreferably about 70 to about 90 wt. %, and more preferably about 75 toabout 85 wt. %.

Hydrophilic monomers that can be employed according to the invention aremonomers that are copolymerizable with the hydrophobic monomer and thatare water soluble. The hydrophilic monomers are selected frommonoolefinic monocarboxylic acids, monoolefinic dicarboxylic acids, ormixtures thereof.

Examples of suitable hydrophilic monomers include, but are not limitedto, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconicacid, crotonic acid, oligomeric acrylic acid, and mixtures thereof. Thecurrently preferred acids are acrylic acid, methacrylic acid, andmixtures thereof.

The amount of hydrophilic monomers based on the total weight of monomers(i), (ii) and (iii) is at least about 1 wt. %, preferably about 2 toabout 10 wt. %, more preferably about 3 to about 10 wt. %, and mostpreferably about 4 to about 8 wt. %.

Partially hydrophilic alkyl acrylate or alkyl methacrylate estermonomers that can be employed according to the invention include alkylacrylate or alkyl methacrylate esters of an alcohol wherein the alkylportion of the alcohol has 1 to 2 carbon atoms. The partiallyhydrophilic monomers can also be referred to as partially water solublemonomers.

Examples of suitable partially hydrophilic monomers include methylacrylate, methyl methacrylate, ethyl acrylate, and mixtures thereof. Thecurrently preferred acids are methyl acrylate, methyl methacrylate, andmixtures thereof, with methyl acrylate being currently most preferred.

The amount of partially hydrophilic monomers based on the total weightof monomers (i), (ii) and (iii) is at least about 5 wt. %, preferablyabout 5 to about 20 wt. %, more preferably about 5 to about 18 wt. %,and most preferably about 10 to about 16 wt. %.

Water-soluble or water-dispersible polymerizable surfactants having aterminal allyl amine moiety that can be employed according to theinvention include those polymerizable surfactants disclosed in U.S. Pat.No. 5,928,783 and U.S. Pat. No. 6,239,240, which are incorporated hereinby reference in their entirety. Preferably, the polymerizablesurfactants of the invention contain a hydrophilic portion selected froma sulfonate allyl amine moiety, a sulfate allyl amine moiety, or aphosphate allyl amine moiety, and a hydrophobic portion selected from—R, or a group having the formula RO—(CH₂CH₂O)_(n)—; wherein R is analkyl group or an alkyl-substituted phenyl group wherein the alkyl grouphas 1 to 20 carbon atoms, preferably 10 to 18 carbon atoms, and n is aninteger from 2 to 100, preferably 2 to 15. The hydrophilic portion andthe hydrophobic portion are connected by means of a covalent bond.Combinations of such polymerizable surfactants can be used in preparingthe polymers of the invention. The water-soluble or water-dispersiblepolymerizable surfactants having a terminal allyl amine moiety useful inthe invention are available from Stepan Company under the Polystep® NMStrademark.

Suitable water-soluble or water-dispersible polymerizable surfactantshaving a terminal allyl amine moiety include, but are not limited to,the following examples.

A preferred polymerizable surfactant is an allyl amine salt of an alkylbenzene sulfonate having the formula

wherein R₁ is an alkyl group having 1 to 20 carbon atoms, preferably 10to 18 carbon atoms, and X⁺ is selected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅,wherein R₄ and R₅ are independently selected from C₁-C₄ alkyl orhydroxyalkyl groups. X⁺ is preferably ⁺NH₃. An example of apolymerizable surfactant of this type is an allyl amine salt ofdodecylbenzene sulfonate.

Another preferred polymerizable surfactant is an allyl amine salt of analkyl ether sulfate having the formula

wherein R₂ is an alkyl group having 1 to 20 carbon atoms, preferably 10to 18 carbon atoms, n is an integer from 2 to 100, preferably 2 to 15,and X⁺ is selected from NH₃ ⁺, ⁺NH₂R₄, or ⁺NHR₄R₅, wherein R₄ and R₅ areindependently selected from C₁-C₄ alkyl or hydroxyalkyl groups. X⁺ ispreferably ⁺NH₃. An example of a polymerizable surfactant of this typeis an allyl amine salt of laureth sulfate.

Another preferred polymerizable surfactant is an allyl amine salt of aphosphate ester having the formula

wherein R₃ is an alkyl or alkyl-substituted phenyl group wherein thealkyl group has 1 to 20 carbon atoms, n is an integer from 2 to 100,preferably 2 to 15, and X⁺ is selected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅,wherein R₄ and R₅ are independently selected from C₁-C₄ alkyl orhydroxyalkyl groups. X⁺ is preferably ⁺NH₃. An example of apolymerizable surfactant of this type is an allyl amine salt ofnonylphenol ethoxylate (9 moles EO) phosphate ester.

Yet another preferred polymerizable surfactant is an allyl amine salt ofa sulfate having the formulaR₆—SO₃ ^(∓)X—CH₂—CH═CH₂wherein R₆ is an alkyl group having 6 to 20 carbon atoms, preferably 10to 18 carbon atoms, and X⁺ is selected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅,wherein R₄ and R₅ are independently selected from C₁-C₄ alkyl orhydroxyalkyl groups. X⁺ is preferably ⁺NH₃.

The substituted phenyl compounds having at least one alkenyl substituentthat can be employed as water-soluble or water dispersible polymerizablesurfactants according to the invention include those disclosed in U.S.Pat. No. 5,332,854, which is incorporated herein by reference in itsentirety.

Suitable substituted phenyl compounds having at least one alkenylsubstituent include compounds having the formula:

wherein R₇ is an alkyl, alkenyl or aralkyl group containing 6 to 18carbon atoms; R₈ is a hydrogen atom or an alkyl, alkenyl or aralkylgroup containing 6 to 18 carbon atoms; R₉ is a hydrogen atom or apropenyl group; A is an unsubstituted or substituted alkylene group of 2to 4 carbon atoms; n is an integer of 1 to about 200, preferably 2 toabout 100; and M is an alkali metal, an ammonium ion or an alkanolamineresidue.

In the substituted phenyl compounds of the invention, the alkyl, alkenyland aralkyl groups of R₇ and R₈ are independently selected and may bethe same or different. Suitable alkyl groups include, but are notlimited to, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl.Suitable alkenyl groups include, but are not limited to, hexenyl,heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl,tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl and octadecenyl.Suitable aralkyl groups include, but are not limited to, styryl, benzyland cumyl.

The propenyl group may occur as trans- and cis-isomers. For the purposesof the present invention, these isomers may be used independently or asa mixture.

For A, suitable unsubstituted or substituted alkylene groups include,for example, ethylene, propylene, butylene, and isobutylene. Thepolyoxyalkylene group -(AO)_(n)— can be a homo-, block or randompolymer, or a mixture thereof.

The conditions of the reaction for producing the substituted phenylsurfactant of the present invention are not critical. For example, thesubstituted phenyl surfactant can be produced by adding an alkyleneoxide such as ethylene oxide (EO) or propylene oxide (PO) to analkylated propenyl phenol in the usual manner, sulfating the addict witha sulfating agent such as sulfuric acid, sulfamic acid, chlorosulfonicacid, or the like, followed by neutralizing with an alkaline substance.

A currently preferred group of substituted phenyl compounds are thosecompounds having the formula:

wherein R₇, A, M and n is as defined above. More preferred compounds arethose wherein R₇ is alkyl, A is ethylene (—CH₂CH₂—), and M is alkalimetal or ammonium. Most preferred compounds are those wherein M isammonium, R₇ is nonyl, and n is about 10 to about 30, such as thecompounds available from Dai-Ichi Kogyo Seiyaku Co., Ltd. (Tokyo, Japan)under the tradename Hitenol BC.

The polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salt compoundsthat can be employed as water-soluble or water-dispersible polymerizablesurfactants according to the invention include those disclosed inJapanese Patent No. JP 2596441 B2 (Dai-Ichi Kogyo Seiyaku Co., Ltd.).

Suitable polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate saltcompounds include compounds having the formula:

wherein R₁₀ is a linear or branched alkyl group containing 8 to 30carbon atoms, preferably 8 to 14 carbon atoms, and more preferably 10 to12 carbon atoms; R₁₁ is hydrogen or methyl, preferably hydrogen; A is anunsubstituted or substituted alkylene group having 2 to 4 carbon atoms;n is 0 or an integer of 1 to about 200, preferably 2 to about 100, morepreferably 2 to about 30; and M is an alkali metal, an ammonium ion, oran alkanolamine residue. Examples of alkanolamine residues includemonoethanolamine, triethanolamine, and the like. 100421 For A, suitableunsubstituted or substituted alkylene groups include, for example,ethylene, propylene, butylene, and isobutylene. The polyoxyalkylenegroup -(AO)_(n)— can be a homo-, block or random polymer, or a mixturethereof.

The polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salt compoundsof the invention can be prepared according to the methods described inJapanese Patent No. JP 2596441 B2.

A currently preferred group of polyoxyalkylene-1-(allyloxymethyl)alkylether sulfate salt compounds are those compounds having the formula:

wherein R₁₀ is an alkyl group containing 8 to 14 carbon atoms, andpreferably 10 to 12 carbon atoms; n is an integer of 1 to about 200,preferably 2 to about 100, more preferably 2 to about 30; and M is analkali metal, an ammonium ion, or an alkanolamine residue. Morepreferred compounds are those wherein R₁₀ is a decyl or dodecyl group, nis 5 to 10, and M is NH₄, such as the compounds available from Dai-IchiKogyo Seiyaku Co., Ltd. (Tokyo, Japan) under the trademark Hitenol® KH.

The total amount of water-soluble or water-dispersible polymerizablesurfactant utilized in the process, e.g. added in steps (a) and (b) ofthe process, based on the total weight of monomers (i), (ii) and (iii)is about 0.1 to about 5 wt. %, preferably about 0.5 to about 2 wt. %.

The amount of water-soluble or water-dispersible polymerizablesurfactant added to the mixture of water, polymerizable surfactant, andpolymerization initiator is that amount effective to produce a latexemulsion having particles having an average particle size of less thanor equal to 200 nm, preferably less than or equal to 100 nm. Theeffective amount needed to obtain the required particle size will bedependent on operating conditions known in the art to have an affect onparticle size, including agitation (shear), viscosity, and the like. Theremainder of the polymerizable surfactant is added with monomers (i),(ii) and (iii). In a preferred embodiment of the invention, the amountof polymerizable surfactant added to the mixture of water, polymerizablesurfactant, and polymerization initiator is at least about 20 wt. % ofthe total amount of polymerizable surfactant added in steps (a) and (b).In the preferred embodiment of the invention, the amount ofpolymerizable surfactant added with monomers (i), (ii) and (iii) is lessthan about 80 wt. % of the total amount of polymerizable surfactantadded in steps (a) and (b).

The process(es) of the invention also utilizes at least onewater-soluble polymerization initiator. Any conventional water-solublepolymerization initiator that is normally acceptable for emulsionpolymerization of acrylate monomers may be used and such polymerizationinitiators are well known in the art. The typical concentration ofwater-soluble polymerization initiators is about 0.01 wt. % to about 1wt. %, preferably about 0.01 wt. % to about 0.5 wt. %, of the totalweight of monomers (i), (ii) and (iii) charged in the pre-emulsion. Thewater soluble polymerization initiators can be used alone or used incombination with one or more conventional reducing agents, such asbisulfites, metabisulfites, ascorbic acid, sodium formaldehydesulfoxylate, ferrous sulfate, ferrous ammonium sulfate, ferricethylenediamine-tetraacetic acid, and the like. Water-solublepolymerization initiators that can be employed according to theinvention include water soluble persulfates, peroxides, azo compoundsand the like, and mixtures thereof. Examples of water soluble initiatorsinclude, but are not limited to, persulfates (e.g. potassium persulfate,and sodium persulfate), peroxides (e.g. hydrogen peroxide, andtert-butyl hydroperoxide), and azo compounds (e.g.4,4′-azobis(4-cyano-pentanoic acid), V-501 from Wako Chemicals).Currently the preferred water soluble polymerization initiators are thepersulfates, particularly potassium persulfate.

The polymerization can be initiated by any conventional method known tothose skilled in the art, such as by application of heat or radiation.The method of initiation will be dependent on the water-solublepolymerization initiator used and will be readily apparent to thoseskilled in the art.

The water soluble polymerization initiator can be added to thepolymerization reaction in any conventional manner known in the art. Itis currently preferred to add a portion of the initiator to the initialreactor charge which comprises water, an effective amount of thewater-soluble or water-dispersible polymerizable surfactant, and aninitial amount of the polymerization initiator. The remainder of theinitiator can be added continuously or incrementally during the emulsionpolymerization. It is currently preferred to incrementally add theremaining initiator.

Following polymerization, the pH of the latex emulsion is adjusted bycontacting the latex emulsion with a suitable base in an amountnecessary to raise the pH to about 6.5 to about 9, preferably about 7 toabout 8. Examples of suitable bases for adjusting the pH of the latexemulsion include alkali metal hydroxides, alkaline earth metalhydroxides, ammonium hydroxide, amines, and the like, and mixturesthereof. The currently preferred base for use in the invention isammonium hydroxide.

The latex emulsion typically has a solids content of from about 40 toabout 70 wt. %, preferably about 45 to about 55 wt. %, and morepreferably about 46 to about 48 wt. %.

In an optional, but currently preferred, embodiment of the invention,the processes of the invention further comprise the addition of a vinylester of a C₂ to C₁₂ aliphatic carboxylic acid to the latex emulsionafter the conversion of monomers (i), (ii) and (iii) is greater than90%, preferably greater than 95%, and more preferably greater than 97%.Typically, this can be accomplished in the processes of the invention byadding the vinyl ester to the latex emulsion after the addition ofmonomers (i), (ii) and (iii) is completed.

Examples of suitable vinyl esters for use in the processes of theinvention include, but are not limited to, vinyl acetate, vinylpropionate, vinyl butyrate, vinyl isobutyrate, vinyl 2-ethylhexanoate,vinyl laurate, the vinyl esters of neo-acids (available from ResolutionPerformance Products under the trademark VeoVa™), and the like, andmixtures thereof The preferred vinyl esters are those that have areactivity similar to the reactivity of the water-soluble orwater-dispersible polymerizable surfactant.

The amount of vinyl ester added to the latex emulsion is about 0.1 toabout 1 wt. %, preferably about 0.2 to about 0.8 wt. %, of the totalweight of monomers (i), (ii) and (iii) charged to the polymerization.

If a vinyl ester is used in the processes of the invention, it iscurrently preferred that additional polymerization initiator be added atthe time of addition of the vinyl ester.

The polymerization reaction can be conducted in any conventionalreaction vessel capable of an emulsion polymerization.

The polymerization can be conducted at a temperature typical foremulsion polymerizations. The polymerization is preferably conducted ata temperature in the range of about 50° C. to about 95° C., preferablyin the range of about 60° C. to about 85° C.

The polymerization time is that time needed to achieve the desiredconversion based on the other reaction conditions, e.g. temperatureprofile, and reaction components, e.g. monomers, initiator, etc. Thepolymerization time will be readily apparent to those skilled in theart.

A third embodiment of the invention relates to pressure sensitiveadhesive compositions having enhanced resistance to water-whiteningcomprising an aqueous emulsion polymer are provided, the polymercomprising the polymerization reaction product of a polymerizableaqueous emulsion comprising: (i) at least one hydrophobic alkyl acrylateor alkyl methacrylate ester of an alcohol, (ii) at least about 1 wt. %of at least one hydrophilic monomer, (iii) at least about 5 wt. % of atleast one partially hydrophilic alkyl acrylate or alkyl methacrylateester of an alcohol, and (iv) a water-soluble or water-dispersiblepolymerizable surfactant selected from compounds having a terminal allylamine moiety, substituted phenyl compounds having at least one alkenylsubstituent, polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfatesalts, or mixtures thereof, wherein the wt. % of monomers (i), (ii) and(iii) are based on the total weight of monomers (i), (ii) and (iii);wherein after the polymerization the pH of the polymer is adjusted to apH of about 6.5 to about 9, and the average particle size of the polymeris less than or equal to 200 nm, preferably less than or equal to 100nm.

In an optional, but currently preferred, embodiment of the invention,the PSA compositions of the invention further comprise a vinyl ester ofa C₂ to C₁₂ aliphatic carboxylic acid, the vinyl ester having been addedto the latex emulsion after the conversion of monomers (i), (ii) and(iii) is greater than 90%, preferably greater than 95%, and morepreferably greater than 97%.

EXAMPLES Abbreviations and Source of Materials

-   2-EHA: 2-ethylhexyl acrylate; Ashland Inc.-   BA: butyl acrylate; Ashland Inc.-   MA: methyl acrylate; Ashland Inc.-   iOA: isooctyl acrylate; Ashland Inc.-   MMA: methyl methacrylate; Ashland Inc.-   AA: acrylic acid; Ashland Inc.-   MAA: methacrylic acid; Ashland Inc.-   Polystep: allylammonium laureth-3-sulfate; Stepan Company-   NMS-7-   Polystep: allylammonium lauryl sulfate; Stepan Company-   NMS-5-   Hitenol BC-2020: 20% active in water, n is about 20; Dai-Ichi Kogyo    Seiyaku Co., Ltd.-   VeoVa 5: vinyl ester of neopentanoic acid; Resolution Performance    Products-   PPS: potassium persulfate; Sigma-Aldrich Co.-   NH₄OH: Ammonium hydroxide (28%); Sigma-Aldrich Co.-   Abex: sulfated nonylphenoxy-poly(ethyleneoxy)ethanol;-   EP-120 Rhodia-   AOT-75: sodium dioctyl sulfosuccinate; Cytec-   Igepal: nonylphenol ethoxylate (with 9 moles of-   Co-630 ethylene oxide); Rhodia-   Mylar: polyester film; DuPont-   Poly H9: release liner; Rexam Release-   Hitenol KH-05: Polyoxyethylene-1-(allyloxymethyl)alkyl ether    sulfate, ammonium salt; Dai-Ichi Kogyo Seiyaku Co., Ltd.

Example 1

In a 2 L jacketed glass reactor equipped with a reflux condenser,thermocouple and twin blade agitator, 701.5 g of polyacrylate latex wasprepared. Monomer pre-emulsion was prepared by mixing 110 g water, 192.4g 2-EHA, 64 g BA, 45 g MA, 6.25 g MAA, and 9.75 g AA with 9.27 gPolystep NMS-7. The reactor was charged with 140 g of water and 3 g ofPolystep NMS-7. Separately, 117 g of PPS stock solution (0.94 wt. %concentration) was prepared in water. The reactor was heated with water.When the temperature reached 79° C., 0.75 g PPS was added followed bycontinuous addition of the monomer pre-emulsion at a 2.1-2.2 g/min ratefor 3.5 hr. The temperature was maintained at 83° C. and thepolymerization charge agitated continuously at 240 rpm. Every 20 min, 10g of the PPS stock solution was added to the reactor. After thepre-emulsion addition was complete, the reactor temperature was raisedto 85° C. and agitated for an additional 40 min after which 1.5 g VeoVa5 was added to the reactor with 5 g of PPS stock solution.

The latex has 47.2% solids. The wt. % solids was determined by placing aknown amount of latex into a weighed aluminum weighing tin, drying at150° C. for 60 min, weighing the tin again and calculating the solidscontent. The average particle size is 80 nm as measured using a Horibalaser scattering particle size distribution analyzer model LA-910. ThepH was 2.34 as measured using an Orion model 250 pH meter. TheBrookfield viscosity is 860 cp using a Brookfield viscometer LV II+ withspindle #3 at 30 rpm.

The latex was then neutralized with NH₄OH to a pH of 7.85.

The neutralized latex was direct coated on a 1 mil Mylar film as well ason Poly H9 release liner. Both films were air dried for 10 min and heatdried at 90° C. for 5 min. The coated Mylar was laminated with releaseliner (direct coat), and the coated release liner was laminated withMylar (transfer coat). For water whitening/water immersion tests, therelease liners were removed thus exposing the polymer surfaces to water.UV/Visible spectroscopy (UV/VIS) using a Cintra 40 UV-Visiblespectrophotometer was used to determine absorbance. The coated Mylarfilm (facestock) was placed in a cuvette which was filled with water attime=0. The light absorbance was measured and recorded for 24 hr at 400nm (room temperature). The final absorbance increase of the direct- andtransfer-coated films was 0.015 and 0.041 respectively (curves # 1 and 2in FIG. 1).

Example 2 Control

In a control experiment, latex was prepared according to the proceduredescribed in Example 1 except conventional surfactants were used inplace of the Polystep NMS-7. Thus, 5.3 g Abex EP-120 (30% solids) wasused in the initial reactor charge, and 3.2 g Abex EP-120, 0.78 g AOT75, and 3.88 g Igepal Co-630 was used to stabilize the pre-emulsion. Thefinal latex had an average particle size of 87 nm, 46.9% solids,pH=2.24, and Brookfield viscosity of 546. The latex was neutralized topH 7.84. The latex film was direct coated as described in Example 1, andthe UV/VIS absorbance was measured in room temperature water during a 24hr immersion test. The final absorbance was 0.388 (curve # 3 in FIG. 1).

The results of Examples 1 and 2 demonstrate that the PSAs of theinvention have significantly improved resistance to water-whiteningcompared to a similar polymer prepared using conventional surfactants.

Example 3

A polymerization was carried out according to the procedure described inExperiment 1 except instead of 2-EHA, 192 grams of iOA was emulsifiedwith BA, MA, AA, and MAA.

The latex had 47.5% solids. The average particle size was 98 nm andpH=2.23. Brookfield viscosity was 740 cp. The latex was neutralized to apH of 7.98 with NH₄OH.

Latex film was prepared by direct coating on Mylar at 1 mil coat weight.The change of absorbance after 24 hr room temperature immersion was0.039.

Example 4

A polymerization was carried out according to the procedure described inExperiment 1 except 16 grams of AA was emulsified with 192 grams of2-EHA, 64 grams of BA, and 45 grams of MA. The polymerization conditionswere identical to those described in Example 1. The latex had 45.4%solids, pH=2.38 and Brookfield viscosity was 572. Average particle sizewas 77 nm. The latex was neutralized to a pH of 7.8 using NH₄OH.

The direct coated film on Mylar has 0.046 absorbance increase after the24 hr room temperature water immersion test.

Example 5

A polymerization was carried out according to the procedure described inExperiment 1 except 45 grams of MMA was emulsified with the describedamounts of 2-EHA, BA, AA, and MAA. The latex had 45.91% solids, pH=2.41,and Brookfield viscosity is 678. The average particle size was 93 nm.The latex was neutralized with NH₄OH to pH=7.95.

The latex film was prepared by direct coating on Mylar as described inExample 1 and tested for water whitening. The absorbance increase after24 hr in room temperature water is 0.024.

Example 6 Comparative

A polymerization was carried out according to the procedure described inExperiment 1 except no partially water soluble monomer i.e., methylacrylate or methyl methacrylate, was used. Thus, the pre-emulsionconsisted of 217 grams of 2-EHA, 84 grams of BA, 6.4 grams of MAA, and9.1 grams of AA emulsified in 110 grams of water with 12.9 grams ofPolystep NMS-7. The latex had 46% solids, pH=2.39, and Brookfieldviscosity was 380. The average particle size was 106 nm. The latex wasneutralized to pH=7.98 using NH₄OH.

The latex film was direct coated on Mylar. The absorbance increase ofthe latex film after 24 hr room temperature water immersion was 0.38.

The results of Example 6 demonstrate that polymerization withoutpartially water soluble monomer produces PSA with unacceptable waterwhitening.

Example 7 Comparative

A polymerization was carried out according to the procedure described inExperiment 1 except 1 gram of Polystep NMS-7 was added to the initialreactor charge. The latex had 47.1 solids, pH=2.76, and Brookfieldviscosity was 348 cp. The average particle size was 119 nm. The latexwas neutralized to pH=7.54 with NH₄OH and direct coated on Mylar. Theabsorbance increase after 24 hr, room temperature water immersion was0.13.

The results of Example 7 demonstrate that polymerization with less thanan effective amount of polymerizable surfactant in the initial reactorcharge produces PSA with unacceptable water whitening and particles withtoo large of an average particle size.

Example 8

A polymerization was carried out according to the procedure described inExperiment 1 except instead of adding 3 grams of Polystep NMS-7, 4.33grams of Polystep NMS-5 was added to the initial reactor charge. Also,the monomer mixture was emulsified with 17.9 grams of Polystep NMS-5.

The latex had 46.5% solids. The particle size was 78 nm, and pH=2.64.The latex was neutralized with NH₄OH to pH=7.49, and coated directly onMylar.

The absorbance increase after 24 hr. room temperature water immersiontest is 0.05.

Example 9

In a 2 L jacketed glass reactor equipped with a reflux condenser,thermocouple and twin blade agitator, a polyacrylate latex was prepared.In a separate vessel, monomer pre-emulsion was prepared by mixing 122.8g water, 298 g 2-EHA, 99.1 g BA, 69.75 g MA, 10.06 g MAA, and 14.08 g AAwith 14.75 g Hitenol BC-2020. The reactor was charged with 296.72 g ofwater, 1.18 g PPS, and 7.37 g of Hitenol BC-2020. Separately, 61.77 g ofPPS stock solution (0.94 wt. % concentration) was prepared in water. Thereactor was heated with water. When the temperature reached 79° C.,continuous addition of the monomer pre-emulsion at a 3 g/min rate wasstarted and continued for 200 minutes. The temperature was maintained at83° C. and the polymerization charge agitated continuously at 240 rpm.Every 20 min for the 200 minute pre-emulsion addition time beginning 20minutes after the start of the pre-emulsion addition, 6 g of the PPSstock solution was added to the reactor. After the pre-emulsion additionwas complete, the reactor temperature was raised to 88° C. and agitatedfor an additional 60 minutes.

The latex has 46.79% solids. The wt. % solids was determined by placinga known amount of latex into a weighed aluminum weighing tin, drying at150° C. for 60 min, weighing the tin again and calculating the solidscontent. The average particle size is 86 nm as measured using a Horibalaser scattering particle size distribution analyzer model LA-910. ThepH was 2.34 as measured using an Orion model 250 pH meter. TheBrookfield viscosity is 1124 cp using a Brookfield viscometer LV II+with spindle #3 at 30 rpm.

The latex was then neutralized with NH₄OH to a pH of 7.85.

The neutralized latex was direct coated on a 1 mil Mylar film. The filmwas air dried for 10 min and heat dried at 90° C. for 5 min. The coatedMylar was laminated with release liner (direct coat). For waterwhitening/water immersion tests, the release liners were removed thusexposing the polymer surfaces to water. UV/Visible spectroscopy (UV/VIS)using a Cintra 40 UV-Visible spectrophotometer was used to determineabsorbance. The coated Mylar film (facestock) was placed in a cuvettewhich was filled with water at time=0. The light absorbance was measuredand recorded for 24 hr at 400 nm (room temperature). The finalabsorbance increase of the direct-coated film was 0.005 whichcorresponds to 98.8% light transmission.

Example 10

In a 2 L jacketed glass reactor equipped with a reflux condenser,thermocouple and twin blade agitator, a polyacrylate latex was prepared.In a separate vessel, monomer pre-emulsion was prepared by mixing 134.5g water, 271.9 g 2-EHA, 90.7 g BA, 63.6 g MA, 9.1 g MAA, and 12.9 g AAwith 5.4 g Hitenol KH-05. The reactor was charged with 364.4 g of water,1.57 g PPS, and 1.35 g of Hitenol KH-05. Separately, 35.5 g of PPS stocksolution (2.5 wt. % concentration) was prepared in water. The reactorwas heated with water. When the temperature reached 79° C., continuousaddition of the monomer pre-emulsion at a 2.94 g/min rate was startedand continued for 200 minutes. The temperature was maintained at 83° C.and the polymerization charge agitated continuously at 240 rpm. Every 20min for the 200 minute pre-emulsion addition time beginning 20 minutesafter the start of the pre-emulsion addition, 3.5 g of the PPS stocksolution was added to the reactor. After the pre-emulsion addition wascomplete, the reactor temperature was raised to 88° C. and agitated foran additional 60 minutes. The latex had 45.8% solids. The wt. % solidswas determined by placing a known amount of latex into a weighedaluminum weighing tin, drying at 150° C. for 60 min, weighing the tinagain and calculating the solids content. The average particle size was76 nm as measured using a Horiba laser scattering particle sizedistribution analyzer model LA-910. The pH was 2.2 as measured using anOrion model 250 pH meter. The Brookfield viscosity was 1200 cp using aBrookfield viscometer LV II+ with spindle #3 at 30 rpm.

The latex was then neutralized with NH₄OH to a pH of 7.12.

The neutralized latex was direct coated on a 1 mil Mylar film. The filmwas air dried for 10 min and heat dried at 90° C. for 5 min. The coatedMylar was laminated with release liner (direct coat). For waterwhitening/water immersion tests, the release liner was removed thusexposing the polymer surface to water. UV/Visible spectroscopy (UV/VIS)using a Cintra 40 UV-Visible spectrophotometer was used to determineabsorbance. The coated Mylar film (facestock) was placed in a cuvettewhich was filled with water at time=0. The light absorbance was measuredand recorded for 24 hr at 400 nm (room temperature). The finalabsorbance increase of the direct-coated film was 0.014. The adhesivewas also exposed to 190° F. water for 10 minutes. After the hightemperature exposure, the no visible color change.

1. A process for preparing a pressure sensitive adhesive having enhancedresistance to water-whitening comprising: (a) forming a polymerizableaqueous pre-emulsion comprising: (i) at least one hydrophobic alkylacrylate or alkyl methacrylate ester of an alcohol, (ii) at least about1 wt. % of at least one hydrophilic monomer, (iii) at least about 5 wt.% of at least one partially hydrophilic alkyl acrylate or alkylmethacrylate ester of an alcohol, and (iv) a water-soluble orwater-dispersible polymerizable surfactant selected from compoundshaving a terminal allyl amine moiety, substituted phenyl compoundshaving at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, wherein the wt. % of monomers (i), (ii) and (iii) are based onthe total weight of monomers (i), (ii) and (iii) in said pre-emulsion;(b) contacting water, an effective amount of a water-soluble orwater-dispersible polymerizable surfactant selected from compoundshaving a terminal allyl amine moiety, substituted phenyl compoundshaving at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, and an initial amount of polymerization initiator to form amixture; (c) continuously adding said pre-emulsion to said mixture topolymerize said pre-emulsion to form a latex emulsion, whereinadditional polymerization initiator is added during the polymerizationof said pre-emulsion; and (d) adjusting the pH of said latex emulsionwith a suitable base to a pH of about 6.5 to about 9; wherein saideffective amount of water-soluble or water-dispersible polymerizablesurfactant in said mixture is that amount necessary to produce saidpressure sensitive adhesive having an average particle size of less thanor equal to 200 nm.
 2. The process of claim 1 wherein the amount ofmonomer (i) in said pre-emulsion is about 70 to about 90 wt. %.
 3. Theprocess of claim 2 wherein the amount of monomer (i) in saidpre-emulsion is about 75 to about 85 wt. %.
 4. The process of claim 1wherein the amount of monomer (ii) in said pre-emulsion is about 2 toabout 10 wt. %.
 5. The process of claim 4 wherein the amount of monomer(ii) in said pre-emulsion is about 4 to about 8 wt. %.
 6. The process ofclaim 1 wherein the amount of monomer (iii) in said pre-emulsion isabout 5 to about 20 wt. %.
 7. The process of claim 6 wherein the amountof monomer (iii) in said pre-emulsion is about 5 to about 18 wt. %. 8.The process of claim 1 wherein said pressure sensitive adhesive has anaverage particle size of less than or equal to 100 nm.
 9. The process ofclaim 1 wherein said monomer (i) is at least one hydrophobic alkylacrylate or alkyl methacrylate ester of an alcohol wherein the alkylportion contains at least 4 carbon atoms.
 10. The process of claim 9wherein said monomer (i) is selected from isooctyl acrylate,4-methyl-2-pentyl acrylate, 2-methylbutyl acrylate, isoamyl acrylate,sec-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isodecylmethacrylate, isononyl acrylate, isodecyl acrylate, or mixtures thereof.11. The process of claim 10 wherein said monomer (i) is selected fromn-butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof.
 12. Theprocess of claim 1 wherein said monomer (ii) is selected from amonoolefinic monocarboxylic acid, a monoolefinic dicarboxylic acid, ormixtures thereof.
 13. The process of claim 12 wherein said monomer (ii)is selected from acrylic acid, methacrylic acid, fumaric acid, maleicacid, itaconic acid, crotonic acid, or mixtures thereof.
 14. The processof claim 13 wherein said monomer (ii) is selected from acrylic acid,methacrylic acid, or mixtures thereof.
 15. The process of claim 1wherein said monomer (iii) is selected from methyl acrylate, methylmethacrylate, ethyl acrylate, or mixtures thereof.
 16. The process ofclaim 15 wherein said monomer (iii) is selected from methyl acrylate,methyl methacrylate, or mixtures thereof.
 17. The process of claim 1wherein the total amount of water-soluble or water-dispersiblepolymerizable surfactant added in steps (a) and (b) is about 0.1 toabout 5 wt. % of the total weight of monomers (i), (ii) and (iii) insaid pre-emulsion.
 18. The process of claim 17 wherein the total amountof water-soluble or water-dispersible polymerizable surfactant added insteps (a) and (b) is about 0.5 to about 2 wt. % of the total weight ofmonomers (i), (ii) and (iii) in said pre-emulsion.
 19. The process ofclaim 17 wherein the amount of water-soluble or water-dispersiblepolymerizable surfactant in said mixture of step (b) is at least about20 wt. % of the total amount of water-soluble or water-dispersiblepolymerizable surfactant added in steps (a) and (b).
 20. The process ofclaim 1 wherein said polymerizable surfactant has a hydrophilic portionselected from a sulfonate allyl amine moiety, a sulfate allyl aminemoiety, or a phosphate allyl amine moiety, and a hydrophobic portionselected from —R, or a group having the formula RO—(CH₂CH₂O)_(n)—;wherein R is an alkyl group or an alkyl-substituted phenyl group whereinthe alkyl group has 1 to 20 carbon atoms, and n is an integer from 2 to100.
 21. The process of claim 20 wherein n is an integer from 2 to 15.22. The process of claim 1 wherein said polymerizable surfactant is anallyl amine salt of an alkyl benzene sulfonate having the formula

wherein R₁ is an alkyl group having 1 to 20 carbon atoms, and X⁺ isselected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅, wherein R₄ and R₅ areindependently selected from C₁-C₄ alkyl or hydroxyalkyl groups.
 23. Theprocess of claim 22 wherein said polymerizable surfactant is an allylamine salt of dodecylbenzene sulfonate.
 24. The process of claim 1wherein said polymerizable surfactant is an allyl amine salt of an alkylether sulfate having the formula

wherein R₂ is an alkyl group having 1 to 20 carbon atoms, n is aninteger from 2 to 100, and X⁺ is selected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅,wherein R₄ and R₅ are independently selected from C₁-C₄ alkyl orhydroxyalkyl groups.
 25. The process of claim 24 wherein n is an integerfrom 2 to
 15. 26. The process of claim 25 wherein said polymerizablesurfactant is an allyl amine salt of laureth sulfate.
 27. The process ofclaim 1 wherein said polymerizable surfactant is an allyl amine salt ofa phosphate ester having the formula

wherein R₃ is an alkyl or alkyl-substituted phenyl group wherein thealkyl group has 1 to 20 carbon atoms, n is an integer from 2 to 100, andX⁺ is selected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅, wherein R₄ and R₅ areindependently selected from C₁-C₄ alkyl or hydroxyalkyl groups.
 28. Theprocess of claim 27 wherein n is an integer from 2 to
 15. 29. Theprocess of claim 28 wherein said polymerizable surfactant is an allylamine salt of nonylphenol ethoxylate (9 moles EO) phosphate ester. 30.The process of claim 1 wherein said polymerizable surfactant is an allylamine salt of a sulfate having the formulaR₆—SO₃ ^(∓)X—CH₂—CH═CH₂ wherein R₆ is an alkyl group having 6 to 20carbon atoms, and X⁺ is selected from ⁺NH₃, ⁺NH₂R₄, or ⁺NHR₄R₅, whereinR₄ and R₅ are independently selected from C₁-C₄ alkyl or hydroxyalkylgroups.
 31. The process of claim 30 wherein R₆ is an alkyl group having10 to 18 carbon atoms.
 32. The process of claim 1 wherein saidpolymerizable surfactant is a substituted phenyl compound having theformula

wherein R₇ is an alkyl, alkenyl or aralkyl group containing 6 to 18carbon atoms; R₈ is a hydrogen atom or an alkyl, alkenyl or aralkylgroup containing 6 to 18 carbon atoms; R₉ is a hydrogen atom or apropenyl group; A is an unsubstituted or substituted alkylene groupcontaining 2 to 4 carbon atoms; n is an integer of 1 to about 200; and Mis an alkali metal, an ammonium ion, or an alkanolamine residue.
 33. Theprocess of claim 32 wherein said polymerizable surfactant is asubstituted phenyl compound having the formula


34. The process of claim 33 wherein R₇ is alkyl, A is ethylene, and M isalkali metal or ammonium.
 35. The process of claim 34 wherein R₇ isnonyl, n is about 10 to about 30, and M is ammonium.
 36. The process ofclaim 1 wherein said polymerizable surfactant is apolyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salt having theformula:

wherein R₁₀ is an alkyl group containing 8 to 30 carbon atoms; R₁₁ ishydrogen or methyl; A is an unsubstituted or substituted alkylene grouphaving 2 to 4 carbon atoms; n is 0 or an integer of 1 to about 200; andM is an alkali metal, an ammonium ion, or an alkanolamine residue. 37.The process of claim 36 wherein said polymerizable surfactant is apolyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salt having theformula:

wherein R₁₀ is an alkyl group containing 8 to 14 carbon atoms; and n isan integer of 1 to about
 200. 38. The process of claim 1 wherein thetotal amount of said polymerization initiator added is about 0.01 toabout 0.5 wt. % of the total weight of monomers (i), (ii) and (iii) insaid pre-emulsion.
 39. The process of claim 1 further comprising theaddition of a vinyl ester of a C₂ to C₁₂ carboxylic acid to said latexemulsion after the conversion of monomers (i), (ii) and (iii) is greaterthan 90%.
 40. The process of claim 39 wherein said vinyl ester is addedto said latex emulsion after the conversion of monomers (i), (ii) and(iii) is greater than 95%.
 41. The process of claim 1 further comprisingthe addition of a vinyl ester of a C₂ to C₁₂ carboxylic acid to saidlatex emulsion after the addition of pre-emulsion is completed.
 42. Apressure sensitive adhesive composition having enhanced resistance towater-whitening comprising an aqueous emulsion polymer preparedaccording to the process of claim
 1. 43. A pressure sensitive adhesivecomposition having enhanced resistance to water-whitening comprising anaqueous emulsion polymer prepared according to the process of claim 39.44. A process for preparing a pressure sensitive adhesive havingenhanced resistance to water-whitening comprising: (a) forming apolymerizable aqueous pre-emulsion comprising: (i) about 70 to about 90wt. % of at least one hydrophobic alkyl acrylate ester selected fromn-butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof, (ii) about2 to about 10 wt. % of at least one hydrophilic monomer selected fromacrylic acid, methacrylic acid, or mixtures thereof, (iii) about 5 toabout 20 wt. % of methyl acrylate, and (iv) a water-soluble orwater-dispersible polymerizable surfactant selected from compoundshaving a terminal allyl amine moiety, substituted phenyl compoundshaving at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, wherein the wt. % of monomers (i), (ii) and (iii) are based onthe total weight of monomers (i), (ii) and (iii) in said pre-emulsion;(b) contacting water, an effective amount of a water-soluble orwater-dispersible polymerizable surfactant selected from compoundshaving a terminal allyl amine moiety, substituted phenyl compoundshaving at least one alkenyl substituent,polyoxyalkylene-1-(allyloxymethyl)alkyl ether sulfate salts, or mixturesthereof, and an initial amount of polymerization initiator to form amixture; (c) continuously adding said pre-emulsion to said mixture topolymerize said pre-emulsion to form a latex emulsion, whereinadditional polymerization initiator is added during the polymerizationof said pre-emulsion; and (d) adjusting the pH of said latex emulsionwith a suitable base to a pH of about 6.5 to about 9; wherein saideffective amount of water-soluble or water-dispersible polymerizablesurfactant in said mixture is that amount necessary to produce saidpressure sensitive adhesive having an average particle size of less thanor equal to 200 nm.